New here and a few questions right away

[Raja_Kentut]

Hello, I am new here in the forum and first would like to introduce myself briefly.
I live in Germany near Nuremberg and work in engineering for a large American electronics company,
registered to get more detailed data of american made Amps than those that can be found on the web only,
am especially interested in the technical data for Fender amplifiers. I love Fenders for their straightforwardness and of course their history.
building tube amps from scratch for a long time, you can see examples here : (unfortunately only in german, but deepl.com is happy to help )

https://www.fingers-welt.de/phpBB/viewt ... 46#p446346
https://www.fingers-welt.de/phpBB/viewt ... ne+cousine

My first questions to you :
What are the exact output voltage and current specifications from the power transformer for the Bassman 5F6-A No. 8087 ? (I want to wind a transformer with the original data, Hammond or the like are quite far off the mark. Helpful would also be a dimensioned drawing and the wire gauges)

Does anyone have the data sheet of the selenium rectifier for the negative bias voltage or knows the forward voltage of it? Yes, a silicon diode will do the job, but selenium ones have far higher forward voltage, I wonder how high?

best regards,

Raja

[Stevem]

Do you have a suitable core to mass wise to wind the PT on?

[Raja_Kentut]

I have access to professional equipment, and advice from a guy who makes his living from building transformers and chokes.
Complicated pieces I buy from a local company that produces individual transformers according to specification.
At home I have also a winding maschine for Pickups and other small coils (from the old Schaller factory), I use it for my CBG pickups.

[Tobyk]

Here you go:

393A18FC-1CC5-418F-8C58-61F057C616A0.jpeg

[Raja_Kentut]

thank you! first time I see the currents in the different paths.
It seems to be very difficult to get any information about the selenium rectifier, those had a very high forward voltage that influences the voltage of the bias winding… not so critical because the resistors can be choosen accordingly, but it is interesting for me.

[Tobyk]

I’d say a forward voltage of about 15V per section. The 5F6-A bias rectifier had 8 sections, so 120V.
Selenium is nasty stuff — a 1N4007 diode can be used instead.

[Raja_Kentut]

Tobyk, that‘s what makes me think…
when just replacing the selenium rectifier with a silicon one, and not adjusting the bias resistors (15k, 56k) you‘ll get a higher bias voltage.
In order to know how to lay out the bias winding in the transformer you need to know the forward voltage….
But, that is not very critical, neverthless one of the things to come near to the original.
What always make me wonder is, how far from the datasheets specs the output tubes are used - and it works wonderfully

[neskor]

It is not a power transformer but OT
https://guitarplayer.ru/equipment-craft ... torov/180/

[martin manning]

... when just replacing the selenium rectifier with a silicon one, and not adjusting the bias resistors (15k, 56k) you‘ll get a higher bias voltage. In order to know how to lay out the bias winding in the transformer you need to know the forward voltage….

A silicon diode and a resistor will sub for the selenium rectifier, and my estimate is that the bias tap voltage was nominally 50VAC. You will certainly have to tweak something to dial the bias in for a given set of output tubes.

[Raja_Kentut]

thank you for the datasheet and the circuit, and thanks to all who have answered!
I‘ll post here when I start this build.
Until then I‘m finishing my current project, a Marshall 2022 preamp/tonestack followed by an EL84 Triode Push Pull powerstage.
I have never seen that combination and am curious how it may sound…

best regards from frankonia,
Raja